5 GHz RF Design

Written by: Brian Petted

Brian has been the Chief Technology Officer at LSR since 2008. He graduated from Milwaukee School of Engineering with a BSEET in 1985, and from Marquette University with a MSEE in 1987. He is the organization’s expert in communications system design and realization and has worked on both commercial and government wireless communications systems.

The number of wirelessly enabled devices has increased dramatically over the past few years. As a result, the single band, 2.4 GHz spectrum has become more crowded than a Los Angeles freeway at rush hour. With four bands and 20 more non-overlapping channels, it’s time to make the move to 5 GHz to ensure your devices work as designed.

5GHz WiFi Channels: Why Now?

Until recently, using the 5 GHz spectrum did not provide any significant benefits in most product applications. With the exponential growth in the adoption and use of wireless devices, however, the 2.4 GHz spectrum is quickly becoming overly crowded. This severely impacts the effectiveness of this spectrum. The growth of WiFi networks, Bluetooth and Bluetooth Low Energy devices, ZigBee networks, microwave ovens, and the wide range of proprietary devices like wireless video cameras, has created significant amounts of interference and leaves little room for additional data capacity in this spectrum.

Figure 1: The very crowded 2.4 GHz band

Medical and industrial customers with critical data requirements have already started the transition to the 5 GHz spectrum to ensure the unfettered transfer of data, but its adoption has been slowed by the lack of cost effective silicon and RF module solutions. This is quickly changing, however, with the recent development and introduction of low cost and easy to implement 802.11 a/b/g/n RF modules. It is now practical to implement 5 GHz solutions for a wide range of product applications.

Where is the 5 GHz Spectrum?

The specific frequencies that apply to the 5 GHz spectrum are broken into four bands providing a whopping 555 MHz of spectrum, with 23 non-overlapping channels versus the paltry 83.5 MHz and three non-overlapping channels at 2.4 GHz.

Band Name

Frequency Band

DFS

UNII-1

5.15 to 5.25 GHz

no

UNII-2

5.25 to 5.35 GHz

yes

UNII-2 Extended

5.47 to 5.725 GHz

yes

UNII-3

5.725 to 5.825 GHz

no

Table 1: 5 GHz bands overview

It is critical to understand the different bands to ensure proper operation in specific applications.

Of the four bands, only UNII-2 Extended is considered usable worldwide. There is also a requirement for Dynamic Frequency Selection (DFS) for specific bands. This requires radar detection capabilities which adds to the complexities involved in the design and EMC certifications for 5 GHz radios. Fortunately, there are certified 802.11 a/b/g/n modules already available that address this for you.

5 GHz Design Considerations

While cordless phone manufactures have successfully used the 5 GHz spectrum for years, most applications for 5 GHz will involve WLAN solutions. A key consideration when using a WLAN at 5 GHz is the need for high performance, dual band antennas. This is due to the reduced range performance resulting from the higher path loss and more severe multi-path at 5 GHz versus 2.4 GHz. Antenna implementation is crucial as well, since it is far more sensitive to the surrounding enclosure and complicated by the fact it needs to operate over a much wider bandwidth.

Another important consideration is that certifying an 802.11 a/b/g/n WLAN device requires testing the radio at the 2.4 GHz band, the four 5.8 GHz UNII bands, and completing DFS testing requirements. Many WLAN silicon solutions also include Bluetooth and Bluetooth Low Energy radio components, which adds two more radios that must be tested and certified. If you add in certifying your product with two antennas, that can be up to 14 different radio combinations that require certification testing, which runs well over $100k in FCC/IC/ETSI testing fees (see Table 2).

Band Name

Transmit

Receive

Radiated

DFS

Base Cost

Additional

Antenna

Conducted

Radiated

2.4 GHz

X

X

X

$10k

$7k

UNII-1

X

X

X

$10k

$7k

UNII-2

X

X

X

X

$11k

$8k

UNII-2 Extended

X

X

X

X

$11k

$8k

UNII-3

X

X

X

$10k

$7k

Bluetooth

X

X

X

$10k

$7k

Bluetooth LE

X

X

X

$10k

$7k

Total

$72k

$51k

Table 2: Estimated EMC Certification Costs

The good news is that cost effective 802.11 a/b/g/n WLAN modules now exist. These include all the certifications and multiple dual band antenna options to make the effective use of the 5 GHz spectrum. LSR’s TiWi5 802.11 a/b/g/n WiFi module is a good example of a FCC/IC/CE certified module, which includes several antenna options for different product enclosures. It is footprint compatible with our popular TiWi-R2 and TiWi-BLE WiFi modules, providing an easy migration from a 2.4 GHz WLAN solution to a 5 GHz WLAN solution. Use of such modules eliminates the need for any additional RF design, antenna design, EMC certifications, and DFS testing for the use of this spectrum.

We highly recommend using the 5 GHz band for your current and future product applications as it has a relatively interference free spectrum with plenty of channel capacity for any of your demanding data applications. It can significantly improve the performance and is a great way to differentiate from your product from your competitors.

LSR has significant expertise in 5 GHz wireless development having integrated it into many products over the past few years. We can assist you in upgrading your product so that it benefits from the many advantages that the 5 GHz spectrum provides.